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Cannot implement some python builtins (eg __getattribute__) in C# class · Issue #2540 · pythonnet/pythonnet · GitHub

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Cannot implement some python builtins (eg __getattribute__) in C# class #2540

Description

Environment

  • Pythonnet version: 3.0.5
  • Python version: 3.10
  • Operating System: Windows 11
  • .NET Runtime: .NET Framework 4.7.2

Details

I have a C# object that I pass into python, and I am trying to implement some python builtins on the C# class. This works fine for some methods, like __repr__() or __dir__(), but runs into issues with __getattribute__. This is an issue as I would like to implement __getattr__ or __getattribute__ for the purposes of customizing attribute access in python for some of my .NET types. https://docs.python.org/3/reference/datamodel.html#object.__getattribute__

I have created a demo C# console application to demonstrate my problem:
MyClass.cs:

namespace pythonnet_demo
{
    internal class MyClass
    {
        public object __repr__()
        {
            return "Test repr!";
        }

        public object __getattribute__(string name)
        {
            return "__getattribute__ works!";
        }

    }
}

Program.cs:

using Python.Runtime;
using System.IO;

namespace pythonnet_demo
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string pythonHome = @"C:\dev\python";
            Runtime.PythonDLL = Path.Combine(pythonHome, "python310.dll");
            PythonEngine.PythonHome = pythonHome;
            PythonEngine.Initialize();

            MyClass obj = new MyClass();

            using (Py.GIL())
            {
                PyModule _scope = Py.CreateScope("__main__");
                _scope.Set("obj", obj);

                //Test repr, works as expected, "Test repr!" printed to console
                _scope.Exec("print(repr(obj))");

                //Test __getattribute__, throws exception, 'AttributeError', no attribute X
                _scope.Exec("print(obj.X)");
            }
        }
    }
}

As noted in the above comments, the __repr__() method from MyClass.cs runs properly from python, but not the __getattribute__ method.

If I create a script.py file and just run it normally via python I do get the expected result.

class MyClassPy:
    def __repr__(self):
        return "Test repr!"
    def __getattribute__(self, name):
        return "__getattribute__ works!"

obj = MyClassPy()
print(repr(obj))
print(obj.X)

The above script prints to the console as expected when run (output below), unlike C# where only the repr method is executed.

Test repr!
__getattribute__ works!

Why doesn't this work from C#? Am I missing something?

Note: I have tried changing the parameters, eg using object name instead of string name in MyClass.cs, same result.

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